Reamer bits for raise boring operations are used for drilling a raise by reaming a pilot hole to the desired final diameter. The drill bit is usually composed of a number of rolling cutters which are arranged in an annular pattern on a raise bit body and are rotated at the same time as the bit is fed upwardly, thus disintegrating the rock around the pilot hole. During the drilling the stem is located in the pilot hole, which has been drilled in advance, and for this reason should have a diameter closely matching the pilot hole. When changing the diameter of the pilot hole and repairing the stem or the bit, it is desirable that the stem be easily detachable and replaceable by a new stem of the same or of a different dimension and that this can be done at the working site by simple hand tools. Also, for transport reasons it is desirable that the stem be detachable.
From U.S. Pat. No. 3,993,147 it is known to provide raise bits with a detachable stem of the above type. The detachable connection disclosed in that patent has, however, been found to have the disadvantage that it is difficult to loosen after drilling for some time, as have other similar connections of a conical type. The effort to loosen the stem is time consuming and must moreover be performed by means of special tools such as hydraulic presses and similar devices.
Considering this background, it is a primary object of the invention to provide a raise bit with a detachable stem which satisfies the requirement of an easily detachable connection between the stem and the bit and also allows a precise fit between the stem and the rest of the bit.